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Open Access Available online http://ccforum.com/content/10/1/R31 Page 1 of 10 (page number not for citation purposes) Vol 10 No 1 Research Clinical relevance of Aspergillus isolation from respiratory tract samples in critically ill patients Koenraad H Vandewoude 1,2 , Stijn I Blot 1,2 , Pieter Depuydt 1 , Dominique Benoit 1 , Werner Temmerman 1 , Francis Colardyn 1 and Dirk Vogelaers 3 1 Department of Intensive Care, Ghent University Hospital, Ghent, Belgium 2 Hogeschool Gent, Health Care Department "Vesalius", Ghent, Belgium 3 Department for Infectious Diseases, Ghent University Hospital, Ghent Belgium Corresponding author: Koenraad H Vandewoude, koenraad.vandewoude@UGent.be Received: 31 Oct 2005 Revisions requested: 8 Dec 2005 Revisions received: 31 Dec 2005 Accepted: 20 Jan 2006 Published: 17 Feb 2006 Critical Care 2006, 10:R31 (doi:10.1186/cc4823) This article is online at: http://ccforum.com/content/10/1/R31 © 2006 Vandewoude et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0 ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Introduction The diagnosis of invasive pulmonary aspergillosis, according to the criteria as defined by the European Organisation for the Research and Treatment of Cancer/ Mycoses Study Group (EORTC/MSG), is difficult to establish in critically ill patients. The aim of this study is to address the clinical significance of isolation of Aspergillus spp. from lower respiratory tract samples in critically ill patients on the basis of medical and radiological files using an adapted diagnostic algorithm to discriminate proven and probable invasive pulmonary aspergillosis from Aspergillus colonisation. Methods Using a historical cohort (January 1997 to December 2003), all critically ill patients with respiratory tract samples positive for Aspergillus were studied. In comparison to the EORTC/MSG criteria, a different appreciation was given to radiological features and microbiological data, including semiquantitative cultures and direct microscopic examination of broncho-alveolar lavage samples. Results Over a 7 year period, 172 patients were identified with a positive culture. Of these, 83 patients were classified as invasive aspergillosis. In 50 of these patients (60%), no high risk predisposing conditions (neutropenia, hematologic cancer and stem cell or bone marrow transplantation) were found. Typical radiological imaging (halo and air-crescent sign) occurred in only 5% of patients. In 26 patients, histological examination either by ante-mortem lung biopsy (n = 10) or necropsy (n = 16) was performed, allowing a rough estimation of the predictive value of the diagnostic algorithm. In all patients with histology, all cases of clinical probable pulmonary aspergillosis were confirmed (n = 17). Conversely, all cases classified as colonisation had negative histology (n = 9). Conclusion A respiratory tract sample positive for Aspergillus spp. in the critically ill should always prompt further diagnostic assessment, even in the absence of the typical hematological and immunological host risk factors. In a minority of patients, the value of the clinical diagnostic algorithm was confirmed by histological findings, supporting its predictive value. The proposed diagnostic algorithm needs prospective validation. Introduction Aspergillus is a saprophytic filamentous fungus widespread in the environment. Although Aspergillus can affect any organ system, the respiratory tract is involved in more than 90% of affected patients. Inhalation of Aspergillus spores or conidia can give rise to various clinical conditions, depending essen- tially on the host's immunological status [1,2]. In immunocom- petent patients, pulmonary aspergilloma, allergic bronchopulmonary aspergillosis and obstructive bronchial aspergillosis are described. In immunocompromised patients, especially with prolonged neutropenia, Aspergillus fumigatus can invade the pulmonary parenchyma, resulting in invasive pulmonary aspergillosis, a disease with a high lethality. More recently, a locally invasive form called necrotizing pulmonary aspergillosis has been described in patients with mild immu- nosuppression [1,3-5]. Recent data indicate that invasive aspergillosis must be considered as an emerging and devas- tating infectious disease in intensive care unit (ICU) patients COPD = chronic obstructive pulmonary disease; EORTC/MSG = European Organisation for the Research and Treatment of Cancer/Mycoses Study Group; ICU = intensive care unit. Critical Care Vol 10 No 1 Vandewoude et al. Page 2 of 10 (page number not for citation purposes) even in the absence of an apparent predisposing immunodefi- ciency. In a carefully designed study in a medical ICU, the inci- dence of invasive aspergillosis was 5.8% ; the majority of these patients did not have a history of hematological malig- nancy. [6]. In an autopsy study of ICU patients, 2.7% of patients were found to have invasive aspergillosis. Chronic obstructive pulmonary disease (COPD) and advanced liver cirrhosis were recognised as potential risk factors [7]. The significance of isolation of Aspergillus from respiratory cultures has been studied extensively in immunocompromised hosts who develop invasive pulmonary aspergillosis [8-10]. On the other hand, little is known about the significance of iso- lation of Aspergillus from respiratory specimens of apparently immunocompetent or mildly immunocompromised patients. Because species of Aspergillus are ubiquitous, one must be cautious in ascribing a pathogenic role to the fungus obtained from a nonsterile site. Therefore, diagnosis of invasive pulmo- nary aspergillosis on the basis of an Aspergillus positive cul- ture from tracheal aspirates remains most difficult in patients with intermediate risk [5], or in patients without currently rec- ognized risk factors. The golden standard for the definite diag- nosis of proven invasive pulmonary aspergillosis remains histopathological lung tissue examination. In clinical practice, the diagnosis of proven invasive pulmonary aspergillosis is rarely established ante-mortem, because of the critical condi- tion of the patients, excluding invasive procedures. Since no non-invasive diagnostic test is sensitive or specific enough to establish definite diagnosis, the diagnostic categories of 'probable' and 'possible invasive pulmonary aspergillosis' have been developed, based on the combination of host risk fac- tors, clinical symptoms and distinct radiological and microbio- logical criteria [11]. These diagnostic criteria were originally developed for clinical trials in patients with bone marrow trans- plants and cancer. However, in ICU patients, clinical signs and symptoms are often non-specific, and except for neutropenia and a congenital or acquired immunocompromised state, it is not feasible to define particular host risk factors, or combina- tions of risk factors, for the acquisition of invasive fungal dis- ease, since there are no large epidemiological studies in this special patient population. The aim of the present study is to assess the clinical relevance of Aspergillus positive respiratory tract samples in ICU patients, based upon a diagnostic algorithm derived from the European Organisation for the Research and Treatment of Cancer/Mycosis Study Group (EORTC/MSG) criteria for inva- sive fungal disease [11] with a modified interpretation of med- ical imaging data and microbiological findings. The validity of the diagnostic criteria was assessed if biopsy or necropsy data were available. Materials and methods Setting The present study was conducted in the Ghent University Hospital, a 1,060 bed primary care and referral centre with a 54 bed ICU including a surgical and medical ICU, an ICU for cardiac surgery and a unit for severely burned patients. Approximately 3,800 patients are admitted to the ICU each year. The surgical ICU serves all kinds of surgery with the need for intensive care management, including multiple trauma and solid organ transplantations. During the study period, 910 patients received a solid organ transplant (kidney, pancreas, liver and heart). The medical ICU serves all patients with internal diseases requiring intensive care, including patients with haematologi- cal malignancies and bone marrow transplant recipients; a total of 270 haematological patients was admitted during the study period. For immunocompromised patients or patients colonized or infected with epidemiologically important micro- organisms, each unit is equipped with several isolation rooms. The burns unit consists of six separated isolation rooms with shower and bath installations within. Study design The study is designed as a historical cohort study (retrospec- tive analysis of prospectively gathered data), including all patients admitted to the ICUs during the period January 1997 through December 2003. The sole criterion for entry in the study is a lower respiratory tract culture positive for Aspergil- lus spp. As a routine practice, all intubated patients in the ICU receive surveillance cultures of endotracheal aspirate thrice weekly. Otherwise, respiratory specimens from all patients, including pulmonary biopsy and specimens of normally sterile sites, are obtained according to the instructions of the attend- ing physicians. The local Center for Hospital Hygiene and Infection Control prospectively files all patient records with any positive culture for Aspergillus spp., hence all relevant data could be retrieved. Patients admitted to the ICU with prior diagnosis of invasive Aspergillus disease were not included in the analysis. Data collection and processing, and patient anonymisation were done according to legal regulations and local Ethics Committee requirements. Given the non-interventional design, the Ethics Committee of the Ghent University Hospital waived informed consent. Definitions of definite or probable invasive pulmonary aspergillosis and Aspergillus colonisation An adapted clinical algorithm considering clinical status, host factors, microbiological data, bronchoscopy with broncho- alveolar lavage, medical imaging and cytological examination of smears of broncho-alveolar lavage fluid results was used to discriminate colonisation from invasive infection. These criteria Available online http://ccforum.com/content/10/1/R31 Page 3 of 10 (page number not for citation purposes) for defining cases of invasive pulmonary aspergillosis are sum- marized in Table 1. For the diagnosis of probable invasive pul- monary aspergillosis, all criteria needed to be fulfilled (1 + 2 + 3 + either 4a or 4b). This algorithm is in part derived from the EORTC/MSG consensus data concerning opportunistic inva- sive fungal infections in immunocompromised patients with cancer and hematopoetic stem cell transplants [11]. The cir- culating galactomannan test for Aspergillus antigen was not routinely available in our institution during the study period, and was hence not taken into the diagnostic elaboration. Patients not fullfilling the criteria for invasive pulmonary aspergillosis were classified as colonized. Autopsy was per- formed at the request of the attending physician after consent of the family. Data collection The following data relevant to patient characteristics were col- lected: age, Acute Physiology and Chronic Health Evaluation (APACHE) II score [12], comorbidities and underlying dis- eases, and treatment with systemic and inhalation corticoster- oids. Data collected concerning ICU treatment and outcome were ICU stay, ventilator dependence, need for vasopressor or inotropic treatment, need for renal replacement therapy, and antifungal therapy. Outcome was described as in-hospital mortality, defined as death within the same hospital episode as the ICU admission. Classification of radiological findings Results of chest X-ray and thoracic CT scan were described as normal, acute respiratory distress syndrome (ARDS)-like, non-specific infiltrates and consolidation, pleural fluid, nodular lesion(s), halo sign, air-crescent sign, and cavitation. The CT halo sign is described as a mass-like infiltrate with a surround- ing halo of ground glass attenuation. The halo lesion was shown to correspond to a central fungal nodule surrounded by Table 1 Criteria for defining cases of invasive pulmonary aspergillosis Definite invasive pulmonary aspergillosis A. Positive result of histological testing and positive result of culture from lung tissue obtained by biopsy or autopsy B. Positive result of culture of a specimen obtained from a normally sterile site by use of aseptic invasive technique Probable invasive pulmonary aspergillosis 1. Aspergillus-positive lower respiratory tract specimen culture 2. Compatible signs and symptoms Fever refractory to at least three days of appropriate antibiotic therapy Recrudescent fever after a period of defervescence of at least 48 hours while still on antibiotics and without other apparent cause Pleuritic chest pain Pleuritic rub Dyspnoea Hemoptysis Worsening respiratory insufficiency in spite of appropriate antibiotic therapy and ventilatory support 3. Abnormal medical imaging by portable chest X-ray or computerised tomography of the lungs 4. Either a. Host risk factors: one of the following conditions Neutropenia (absolute neutrophil count less then 500/mm 3 ) preceding or at the time of ICU admission Underlying haematological or oncological malignancy treated with cytotoxic agents Glucocorticoid treatment (prednisone or equivalent, >20 mg/day) Congenital or acquired immunodeficiency Or b. Semiquantitative Aspergillus-positive culture of BAL (+ or ++), without bacterial growth together with a positive cytological smear showing branching hyphae Aspergillus colonisation Not fullfulling the criteria for proven or probable invasive pulmonary aspergillosis ICU, intensive care unit; BAL, broncho-alveolar lavage. Critical Care Vol 10 No 1 Vandewoude et al. Page 4 of 10 (page number not for citation purposes) a rim of hemorrhage and coagulative necrosis. The air-cres- cent sign is described as a pulmonary cavitation [13,14]. Other definitions Acute renal failure is defined as the need for renal replacement therapy, acute respiratory failure as the need for acute mechanical ventilation and cardiovascular failure as the need for inotropic or vasopressive support despite adequate fluid resuscitation [15-18]. Statistics Continuous variables are described as median (interquartile range). Comparative analyses were performed with the Mann- Whitney U or Chi-square test when appropriate. Survival curves were prepared by means of the Kaplan-Meier method and univariate survival distributions were compared with use of the Log rank test. Statistical analyses were performed with SPSS 11.0 (SPSS Inc., Chicago, IL, USA). All used tests are two-tailed and statistical significance is defined as P < 0.05. Figure 1 Diagnostic breakdown of the study cohort (172 patients)Diagnostic breakdown of the study cohort (172 patients). Available online http://ccforum.com/content/10/1/R31 Page 5 of 10 (page number not for citation purposes) Results During the observation period, 25,216 patients were admitted to the ICU. Respiratory tract samples were positive for Aspergillus in 172 patients (incidence: 6.8/1,000 ICU admis- sions). The diagnostic breakdown of the cohort is illustrated in Figure 1. According to the predefined criteria, 83 cases (48.3%) were classified as invasive pulmonary aspergillosis (17 definite, 68 probable). In the remaining 89 patients (51.7%), the presence of Aspergillus was considered as col- onisation. Pulmonary biopsy was performed in ten patients. Biopsy was positive in seven patients, who were classified as documented invasive aspergillosis ante-mortem. In three patients, classified clinically as colonisation, lung biopsy showed no fungal disease. Autopsy in patients with an Aspergillus positive respiratory tract specimen was performed in 16 patients. Ten of these patients fullfilled the predefined criteria of probable invasive pulmonary aspergillus ante-mor- tem; since lung necropsy specimens confirmed the diagnosis, they were subsequently classified as definite invasive pulmo- nary aspergillosis. In six patients who were considered as col- onized ante-mortem, the autopsy did not reveal invasive Aspergillus disease. In Table 2, underlying conditions of patients with invasive pul- monary aspergillosis and colonisation are summarized. Of the patients diagnosed with invasive pulmonary aspergillosis, Table 2 Underlying diseases in intensive care unit patients with respiratory tract samples positive for Aspergillus spp. Underlying condition Associated with invasive aspergillosis a Associated with Aspergillus colonisation Hematological malignancy b 28 (2) 3 With neutropenia 6 (1) 1 Post bone marrow/stem cell transplantation 2 0 Myelodysplastic syndrome 4 - Solid tumor with chemotherapy 3 1 Solid tumor without chemotherapy 5 3 Graves' disease - 1 Immunosuppressive therapy 14 (4) 8 Solid organ transplant 8 (2) 4 Auto-immune disease 4 (2) 4 Lung fibrosis 2 0 Aplastic anemia 1 1 Chronic obstructive pulmonary disease 29 (4) 25 Requiring chronic systemic corticosteroid use 21 (3) 12 Requiring inhalation corticosteroids 24 (3) 16 Asthma 2 1 Liver cirrhosis 3 (2) 2 Malnutrition 3 - Diabetes mellitus 8 (1) 9 Alcoholism 5 (2) 3 Chronic heart failure 6 5 Chronic renal failure – dialysis dependent 3 (1) 2 Lung fibrosis 2 1 Active Cytomegalovirus disease 3 1 Active tuberculosis - 1 Absence of known underlying disease 14 (5) 27 a Numbers in parentheses indicate cases with definite invasive aspergillosis. b P value < 0.05 for difference between patients with invasive aspergillosis (definite + probable) and colonisation. Critical Care Vol 10 No 1 Vandewoude et al. Page 6 of 10 (page number not for citation purposes) 40% of patients had a high risk profile (neutropenia, hemato- logical cancer, bone marrow or stem cell transplant). Patient characteristics and outcome are summarised in Table 3. Tho- racic medical imaging (Table 4) shows that nodular lesions were almost exclusively found in invasive pulmonary aspergil- losis (30% versus 2%; P < 0.001). The halo and air-crescent sign were evident in only three patients. Most patients classi- fied as invasive pulmonary aspergillosis had non-specific radi- ological findings. Appropriate antifungal treatment was given to 71 (85.5%) patients with invasive pulmonary aspergillosis. All patients classified with invasive pulmonary aspergillosis in whom no antifungal therapy was started died (n = 12). When these patients were excluded, the mortality rate was 73%. Figure 2 shows the survival curves of patients categorised as invasive aspergillosis and colonisation. Discussion Until recently, research on epidemiology and risk factors for the acquisition of Aspergillus infection and treatment of inva- sive disease has almost enterily focused on severely immuno- compromised patients with hematological malignancy and solid organ recipients. However, recent literature indicates an expanding spectrum of patients at risk for invasive aspergillus disease. These are categorised into high risk (allogeneic bone marrow transplant, neutropenia and hematological cancer), intermediate risk (autologous bone marrow transplant, malnu- trition, corticosteroids, HIV, solid organ transplant, diabetes, underlying pulmonary disease and solid organ cancer) and low risk (cystic fibrosis and connective tissue disease) [5]. Further- more, case reports and papers about invasive pulmonary aspergillosis in COPD patients and apparently non-immuno- compromized patients [19-26] have been published. Hence, it seems worthwile to address the question of diagno- sis of invasive pulmonary aspergillosis in ICU patients. The lack of validated and stringent criteria for case definitions in patient categories, other than hemato-oncological and solid organ transplant, hampers diagnostic assessment. The ante- mortem diagnosis of proven invasive aspergillosis is extremely difficult to establish in ICU patients as hemodynamic and/or respiratory insufficiency and coagulopathy often preclude invasive tissue sampling. Because of these diagnostic limita- tions, a feasible diagnostic approach was developed. As in the EORTC/MSG definitions, host factors for the acquisition of invasive disease were taken into account. For patients who did not meet the criteria for high-risk host, the Aspergillus spp. positive tracheal aspirate had to be corroborated with a posi- tive semi-quantitative culture and a positive cytological exami- Table 3 Patient characteristics for intensive care unit patients with invasive pulmonary aspergillosis and Aspergillus colonisation Characteristic Definite invasive aspergillosis (n = 17) Probable invasive aspergillosis (n = 66) Invasive aspergillosis (n = 83) Aspergillus colonisation (n = 89) P a Age (years) 54 (51–63) 61 (50–69) 61 (51–69) 66 (47–72) 0.186 APACHE II score 28 (21–30) 28 (20–31) 28 (19–34) 24 (20–29) 0.021 Neutropenia 3 (17.7) 8 (12.1) 11 (13.3) 2 (2.2) 0.008 Hemodynamic instability 17 (100) 49 (74.2) 74 (89.2) 58 (65.2) < 0.001 Acute renal failure 10 (58.8) 23 (34.9) 33 (39.8) 23 (25.8) 0.073 Acute respiratory failure 17 (100) 63 (95.5) 80 (96.4) 77 (86.5) 0.029 Duration of mechanical ventilation prior to first positive culture (days) 2 (1–8) 4 (1–9) 3 (1–8) 3 (1–7.5) 0.690 Duration of mechanical ventilation (days) 11 (6–24) 15 (6–32) 13 (5–29) 9 (3–21) 0.031 Length of ICU stay prior to first positive culture (days) 2 (1–8) 4 (1–9) 4 (1–8) 5 (1–9) 0.396 Length of ICU stay (days) 11 (7–24) 15 (7–34) 14 (7–31) 13 (6–25) 0.383 Number of cultures positive for Aspergillus spp. 2 (2–3.5) 2 (2–3) 2 (2–3) 1 (1–2) < 0.001 Number of patients examined with BAL 12 (70.6) 49 (74.2) 61 (73.5) 29 (32.6) < 0.001 28-days mortality 15 (88.2) 44 (66.7) 59 (49.0) 26 (23.1) < 0.001 In-hospital mortality 16 (94.1) 48 (72.7) 64 (77.1) 36 (40.4) < 0.001 Continuous variables are described as median (interquartile range); categorical variables are described as n (%). a P value for invasive aspergillosis (n = 83) versus Aspergillus colonisation (n = 89). No significant differences were observed between patients with proven versus probable invasive aspergillosis. APACHE, Acute Physiology and Chronic Health Evaluation; ICU, intensive care unit; BAL, broncho-alveolar lavage Available online http://ccforum.com/content/10/1/R31 Page 7 of 10 (page number not for citation purposes) nation of broncho-alveolar lavage fluid. This is in part endorsed by the observations of Greub and Bille [27] in a case-definition study in immunocompromised patients: compared to those from patients considered to be colonised, cultures of lower respiratory tract specimens from patients with proven invasive pulmonary aspergillosis showed a significant difference in the total number of Aspergillus colonies recovered from culture per episode; for BAL (broncho-alveolar lavage), the number of Aspergillus colonies per agar plate was also significantly higher in the proven aspergillosis group. Furthermore, many authors consider the visualisation of the characteristic septate hyphae in bronchial washings as a confirmatory finding of inva- sive disease in the presence of a compatible clinical picture [8,28-32]. False-positive results appear to be unusual, since patients without chronic lung diseases rarely show colonisa- tion of the lower tracheobronchial tree with Aspergillus [33]. Compared to the EORTC/MSG diagnostic criteria, the inter- pretation of radiological data in the algorithm is also less strict, as any major radiological sign of pneumonia is taken into con- sideration. Medical imaging of the thorax in ICU patients is less pathognomonic due to many confounding factors such as ven- tilator associated pneumonia, atelectasis, and pleural fluid effusions in critically ill ventilated patients; furthermore, it can be speculated that typical radiological lesions may be less apparent because of the difference in severity and nature of the immune derangements. Typical lesions for invasive aspergillosis, such as the halo and the air-crescent sign, were only found in 5% of patients. This is in agreement with the low sensitivity of 24% in patients without hematological malig- nancy compared with 82% in patients with neutropenic hema- tological malignancy [34]. Since the modified clinical diagnosis of probable invasive aspergillosis is less stringent than the EORTC/MSG criteria, a lower specificity may be of concern. However, in a limited number of patients, histopathological specimens were availa- ble in order to check the validity of the clinical assumption. Samples for histology were available in 26 patients. Of these, 13 fullfilled the EORTC/MSG criteria for host risk factors. Ten patients underwent pulmonary biopsy. Seven of these met the criteria of probable aspergillosis prior to biopsy, and could be reclassified ante-mortem as definite invasive pulmonary aspergillosis because of a positive histopathological examina- tion. In three other patients, classified as colonized, lung biopsy showed no evidence of fungal infection. Furthermore, autopsy data were available in 16 patients, of whom 10 were classified as probable invasive pulmonary aspergillosis ante- mortem, and the other six patients as colonized. Necropsy findings histologically confirmed the clinical diagnosis in all these patients. These data are in support of a high positive predictive value of the criteria for the diagnosis of invasive pul- monary aspergillosis. Nevertheless, the number of patients with histological confirmation was low. The true predictive value of the proposed diagnostic algorithm needs to be assessed prospectively. In this study, using an entry criterion of an Aspergillus positive respiratory specimen and an adapted diagnostic algorithm, an incidence of invasive pulmonary aspergillosis of 3.2/1,000 ICU admissions was found. In the subgroup of medical patients, the incidence was three times as high (10.2/1,000). In a recent retrospective study in a medical ICU, an incidence of invasive aspergillosis of even 5.8% was found, with, in most cases, pulmonary involvement [6]. In a study considering autopsies of patients from a mixed medical-surgical ICU, an incidence of 2.7% of proven invasive aspergilosis was found [7]. In general, the autopsy rate is low in our institution (<5%) because of local ethical regulations. It can not be excluded that patients classified as colonized indeed had invasive dis- ease, and that other patients with negative surveillance cul- tures suffered from invasive disease since respiratory tract cultures lack sensitivity. It is clear that a stringent protocol for post-mortem examination is necessary for a truthful estimation of the epidemiology and incidence of invasive aspergillosis in Table 4 Radiological findings in intensive care unit patients with invasive pulmonary aspergillosis or Aspergillus colonisation Radiological finding Invasive aspergillosis (n = 83) a Aspergillus colonisation (n = 89) Normal b 030 Diffuse reticular or alveolar opacities (ARDS like) b 12 (1) 4 Non-specific infiltrates and consolidation 42 (10) 49 Pleural fluid 0 5 Nodular lesions b 25 (5) 1 Air-crescent sign 1 0 Halo sign 2 (1) 0 Cavitation 1 0 a Numbers in parentheses indicate cases with definite invasive aspergillosis. b P value < 0.05 for differences between the groups. ARDS, acute respiratory distress syndrome. Critical Care Vol 10 No 1 Vandewoude et al. Page 8 of 10 (page number not for citation purposes) ICU patients [6,7]. Furthermore, prospective research should include non-culture methods for diagnosis, such as the detec- tion of galactomannan, PCR, and beta-D-glucan in non-neutro- penic patients [35,36]. At this time, it is unclear if these non- invasive methods are of any diagnostic value in critically ill patients without the EORTC/MSG host risk factors. An important finding is that the majority of the patients classi- fied as having invasive pulmonary aspergillosis did not belong to the well known high-risk group (neutropenia, bone marrow transplant, hematological cancer); this is in accordance with the data provided in the study by Meersseman and colleagues [6]. Underlying conditions, such as COPD, chronic lung dis- ease, non-hematological malignancy, HIV infection, diabetes mellitus, liver failure, chronic alcohol abuse, malnutrition and extensive burns, have been described in association with inva- sive aspergillosis [5,7,37,38]. In the EORTC/MSG diagnostic criteria, the use of corticosteroids for more than three weeks is considered a predisposing host factor [11]. In the setting of persistent septic shock, steroids are frequently used since a beneficial effect has been demonstrated [39]. Corticosteroids substantially impair macrophage killing of Aspergillus spores and mononuclear cell killing of Aspergillus hyphae [40]. In the setting of underlying lung disease, there is a risk factor for inva- sive aspergillosis at much lower doses and shorter courses of steroids [41,42]. This should be taken into account in the clin- ical assessment of an Aspergillus spp. positive respiratory tract sample. Steroid treatment has also been given important weight in a recently described point-score system for assess- ment of positive cultures [43]. It has been speculated that patients with normal immune function prior to ICU admission may be at risk for invasive aspergillosis due to a temporary immunoparalysis in the context of the multiple organ dysfunc- tion syndrome [44]. Hospital mortality of patients with invasive pulmonary aspergil- losis in this study was high (77%), but in accordance with pre- vious reports describing dramatic fatality rates [22,24,45,46]. When comparing the survival curves of the group of patients with invasive aspergillosis with the group of patients classified as colonised, a clear difference is observed during the first 15 days after positive respiratory Aspergillus culture and fullfill- ment of the diagnostic criteria for invasive disease. The initial decline of the curve of patients with invasive disease is more pronounced, reflecting an acute mortality probably due to Aspergillus infection. This fits well with the generally accepted time frame of the development of invasive Aspergillus disease until demise. This observation is an indirect argument in favour of the value of the diagnostic algorithm. Conclusion The finding of an Aspergillus positive respiratory tract sample in an ICU patient cannot be discarded and must trigger further diagnostic exploration using BAL, with semiquantitative cul- ture and cytological examination, as well as CT scan and pul- monary biopsy if possible. Adapted clinical diagnostic criteria should be used in order not to miss a critical window of thera- peutic opportunity. The proposed diagnostic algorithm for the diagnosis of inva- sive pulmonary aspergillosis is supported by histopathological data from a subgroup of patients. An important finding is that not only patients with severe hematological disease are afflicted: the majority of patients has an intermediate risk for the acquisition of invasive disease. Radiological features are often non-specific. The associated mortality is high in spite of appropriate treatment. Competing interests The authors declare that they have no competing interests. Authors' contributions KV, WT and DV conceived and designed the study. Acquisi- tion of the data was performed by KV and WT. Statistical anal- ysis was performed by SB and PD. Interpretation of the results was done by KV, SB, DV, FC and PD. KV and SB drafted the manuscript, after which it was revised by DV, PD, FC and DB. Acknowledgements The authors thank Prof. Dr G Verschraegen, MD, and Mr P Dewaegem- aeker, MA, from the Hospital Hygiene Team of the Ghent University Hos- pital, for kindly providing data from the Aspergillus registry. This paper has been partially presented at the 44th Interscience Conference on Antimicrobial Agents and Chemotherapy, Washington, USA, 30 Octo- ber to 2 November, 2004. Figure 2 Survival curves for intensive care unit patients with invasive pulmonary aspergillosis and Aspergillus colonisation (Log rank test: P < 0Survival curves for intensive care unit patients with invasive pulmonary aspergillosis and Aspergillus colonisation (Log rank test: P < 0.001). Patients with invasive aspergillosis are represented by the solid line; patients with Aspergillus colonisation are represented by the dashed line. Available online http://ccforum.com/content/10/1/R31 Page 9 of 10 (page number not for citation purposes) References 1. Sharma OP, Chwogule R: Many faces of pulmonary aspergillo- sis. Eur Respir J 1998, 12:705-715. 2. Barnes AJ, Denning DW: Aspergilli – significance as pathogens. Rev Med Microbiol 1993, 4:176-180. 3. Denning DW: Invasive aspergillosis. Clin Infect Dis 1998, 26:781-803. 4. Saraceno JL, Phelps DT, Ferro TJ, Futerfas R, Schwartz DB: Chronic necrotizing pulmonary aspergillosis: approach to management. Chest 1997, 112:541-548. 5. 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J Hosp Infect 2004, 56:269-276. . significance of isolation of Aspergillus spp. from lower respiratory tract samples in critically ill patients on the basis of medical and radiological files using an adapted diagnostic algorithm. colonisation An adapted clinical algorithm considering clinical status, host factors, microbiological data, bronchoscopy with broncho- alveolar lavage, medical imaging and cytological examination of. epidemiology and incidence of invasive aspergillosis in Table 4 Radiological findings in intensive care unit patients with invasive pulmonary aspergillosis or Aspergillus colonisation Radiological finding